Protective system for vapor electric devices



Oct. 14, 1941. J. SLEPIAN ETAL 2,259,329

PROTECTIVE SYSTEM FOR VAPOR ELECTRIC DEVICES Filed Aug. 2, 1940 WITNESSES:

INVENTORS Jaseph .SZapz'an and Jo s eph H. 001.

JJJW

ATTORNEY simultaneously energizes a Patented Oct. 14, 1941 Joseph Slepian,

TRIO DEVICES Pittsburgh, and Joseph H. Cox,

Forest Hills, Pm, assignors to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa.,

a corporation of Pennsylvania Application August 2, 1940, Serial No. 349,657

1 Claim.

Our invention relates to a vapor electric device, and particularly to a control system for a make-alive type converter.

In the operation of vapor electric devices such as mercury arc rectiflers there are occasional or random faults such as are back or internal short circuits which make it desirable to momentarily interrupt the operation of the device in order to regain normal control of the operation.

In the operation of make-alive type converters it has heretofore been proposed to momentarily interrupt the operation of the device by blocking the auxiliary control tubes which supply the impulses of potential for initiating the oathode spot in the individual valves. However, we have found that in many cases the interruption of the control impulse is not suflicient to interrupt the fault current in the valves. In modern high power make-alive valves it has been found desirable to apply shields to the anodes which optically obscure the anode from the active cathode area. We have discovered that if shields are applied to the anodes, it is desirable to apply positive potential to the shields in order to insure proper pick up of the current carrying arc to the main anode of the valve.

- In the control system according to our invention, we have utilized these control shields for insuring blocking of the arc in theindividual valves of a converter undergoing are back or internal short circuit.

In the system according to our invention, a relay responsive to fault current in the makealive type devices operates a relay which applies a negative bias suflicient to interrupt the periodic flow of current to the make-alive electrodes and relay which applies negative potential to the shields of each of the valves so that all of the valves are rendered inoperative for a suflicient length of time to regain normal control of the converter.

It is aprimary object of our invention to provide a control system for a vapor electric device in which the operation of the device is momentarily interrupted in response to fault currents in the device.

It is a further object of our invention to provide a means for supplying control potential to the anode shields of a vapor electric device of the make-alive type.

Other objects and advantages of our invention will be apparent from the following detailed description taken inconiunction with the acis a schematic illustration of a vapor electric device according to our invention.

In the exemplary embodiment according to ourinvention, a direct-current circuit l is connected to an alternating current circuit 2 by means of a suitable connecting transformer 3 and the flow of current through the transformer 3 is controlled by means of a plurality of make-alive type valves 4. Each of the make-alive type valves 4 includes a vaporizable cathode 5 of suitable material, such as mercury, a cooperating anode 6,. a shield l substantially surrounding the anode 6 and a make-alive electrode 8 in permanent contact with the vaporizabl cathode 5.

Control potentials are supplied to the several make-alive electrodes by an impulsing system herein shown as composed of a control transformer 8 for supplying the energy for the makealive electrodes 8 through suitable grid controlled tubes ill, the grids 35 of which are in turn energized by a grid transformer l5.

The application of the control potentials to the make-alive electrodes 8 is controlled by means of suitable auxiliary rectifying devices such as the control tubes i0. Preferably, energy storing devices such as capacitors H are connected across each of the phase windings 12 of the control transformer 9 in order to improve the characteristic of the impulse potential and to reduce the firing energy required. Suitable impedances, suchas resistors Hand [4 are used to control the flow of current into and out of the energy storing capacitors H. i

The control tubes I0 are grid controlled from a suitable source of potential such as grid transformer IS, the phase of which may be controlled by means of a suitable phase shifter, such as the rotary phas shifter I 6, illustrated as connected between the grid transformer l5 and a suitable source of supply such as the alternating current circuit 2.

In order to insure pickup of the main arc in each of the valves 4, means are provided for connecting a suitable potential to the shields 1. This potential may be applied from any suitable synchronized source such as the shielded anode,

from any suitable source but herein we have provided the biasing potential by means of a transformer 2| connected to a rectifying device 22, the output of which is connected across a potentiometer 23. If desired suitable filtering circuits 24 may be connected to the rectifying device 22.

Current transformers 25 associated with the responsive relay 5|. Also, the biasing relay 3| is normally open so that control potential is applied to the anode shields I from any suitable source and the grid transformer I5 periodically energizes the control grids 35 of the firing tubes III to periodically initiate operation of the makealive type valves 4. However, in the event of a fault the fault relay 5i picks up, opening its back contact 28 and closing its front contact 30. thus applying negative bias to the grid transformer l5 to block the firing tubes l0 and thus the control impulses to the make-alive electrodes 8. At the same time, the biasing relay 3| picks contact 28 of the fault relay Bl to the mid tap 29 in the grid transformer l5.

Upon the occurrence of a fault, the fault relay 5! picks up opening its back contact 22 and closing its front contact 30 so that the negative biasing potential is applied between the cathode 5 of the valves 4 and the mid tap 29 of the grid transformer iii. The pick up of the fault relay 5| supplies the biasing potential to the shields I of the several valves t so that these shields are maintained at a negative potential during the interval that the negative bias on the firing trans-- former l 5 blocks the operation of the firing tubes l0 and thus prevents the application of control impulses to the make-alive electrodes 8. Preferably the application of the biasing potential to the shields I is accomplished by an auxiliary relay 3i connected across a suitable source such as the biasing potential source 22 so that sufficient power 'is available for actuation of the contact up its contacts 32 applying negative potential to the anode shields I, thus blocking completely the operation of the vapor electric device; If desired either the fault responsive relay Si or the biasing relay 3i, or both, may be of the fast closing slow opening type or of the time controlled type, so that any suitable time interval shut-down of the converter may be secured.

While for purposes of illustration we have shown and described a specific embodiment of our invention, it is apparent that changes and modifications can be made therein without departing. I

from thetrue spirit of our invention or the scope of the appended claim.

We claim as our invention:

In a vapor electric converter of the make-alive. type having a plurality of make-alive type valves,

' for controlling the firing tubes, a source of control potential connected to the anode shields, a source of biasing potential, a fault responsive relay for applying said biasing potential to said firing'transformer for blocking said firing tubes, an auxiliary relay energized from said source of biasing potential through said fault responsive 

